This is the easiest step of all, and it won't really take any extra time: buy mainstream products that also happen to be gluten-free.
Gluten-free cereal is a great example of this: Multiple gluten-free cold cereals and gluten-free kids' cereals actually are products of mainstream brands and carry mainstream price tags. Your gluten-free options include several General Mills' Chex cereals, Post Fruity and Cocoa Pebbles, and Kellogg's Rice Krispies (just make sure not to buy the wrong Rice Krispies box — the gluten-containing version is still for sale, too).
Check out your potato chip and corn chip selections, too — plenty of brands, including some really mainstream ones like Frito-Lay, are offering gluten-free potato chips and gluten-free tortilla chips. I've also seen gluten-free crackers (usually rice crackers) in the "mainstream" section of the supermarket, for a reasonable price.
If you crave a sweet snack, there's plenty of mainstream gluten-free candy available, too.
Some yogurt brands have begun to sport gluten-free labels (make sure to check ingredients carefully, since not all yogurts are safe), and other foods, such as some prepared rice mixes, also are marked "gluten-free." Most of these will be less-expensive alternatives to specialty gluten-free food products, such as breads, cookies and frozen foods — see my overall Gluten-Free Food List article for more information on what's safe and what's not.
By buying only "mainstream" brands and avoiding gluten-free specialty products as much as possible, you potentially can save as much as 30% to 50% every time you buy those types of products.